Automatic tracing device



Sept. 5, 1961 'r. E. DUGLE ETAL 2,998,759

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 sheets sheet jgZ 36 9 48 O=O 0 I 37 584 800 08 I no 5 3 5 9 INVENTORS THOMAS E. DUGLELOREN J. MEYERS BY DES JARDINS, ROBINSON & KEISER THEIR ATTORNEYS p 5,1961 5,. DUGLE ET AL 2,998,759

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 Sheets'sheet 2TH EIR ATTOR N EYS Sept. 5, 1961 T..E. DUGLE ET AL AUTOMATIC TRACINGDEVICE 9 Sheets-Sheet 5 Original Filed July 15, 1955 INVENTORS THOMAS E.DUGLE LOREN J. MEYERS BY DES JARDIN5,ROBINSON & KEISER TH EIR ATTOR NEYS pt 5, 19 DUGLE ETAL 2,998,759

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 SheetsSheet 4NVENTORS THOMAS E. DUGLE LOREN J. MEYERS Y DES fARDINS, ROBINSON &KEISER TH El R ATTORNEYS Sept. 5, 1961 DUGLE ET AL AUTOMATIC TRACINGDEVICE 9 Sheets-Sheet 5 Original Filed July 15, 1955 r FIL.

TH EIR ATTOR N EYS Sept. 5, 1961 T. DUGLE ET AL AUTOMATIC TRACING DEVICE9 Sheets-Sheet E. DUGLE LOREN J. MEYERS IN V EN TORS THOMAS TH El RATTORNEYS BY DES JARDINS, ROBINSON 8. KEISER Original Filed July 13,1955 Sept. 5, 1961 T. E. DUGLE ET AL AUTOMATIC TRACING DEVICE 9Sheets-Sheet '7 Original Filed July 13 1955 INVENTORS THOMAS E. DUGLELOREN J. MEYERS DES JARDIN$,ROBINSON & KEISER TH El R ATTOR N EYS nnmSept. 5, 1961 T. E. DUGLE ET Al. 2,998,759

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 Sheets-Sheet 9(O Q 9, K" 8 n 1 *3 I s 8 5 28 z 5 w v w w INVENTORS THOMAS E. DUGLELOREN J. MEYERS BY DES JARDINS, ROBINSON & KEISER THEIR ATTORNEYSApplication Sept. 11, 1958, Ser. No. 761,277, now Patent No. 2,949,739,dated Aug. 23, 1960, which is a continuation of application Ser. No.521,795, July 13, 1955, now abandoned. Divided and this application Mar.21, 1960, Ser. No. 17,240

3 Claims. ((31. 90-62) This application is a division of our co-pendingpatent application, Serial No. 761,277, filed September 11, 1958 for anAutomatic Tracing Device, now Patent 2,949,739, issued August 23, 1960.The latter application is a continuation of application, Serial No.521,795, filed by us on July 13, 1955, and now abandoned.

The present invention relates to a tracer control mechanism of the typein which a finger or stylus is automatically caused to follow theoutline of a pattern through a full 360 degrees of movement of thefinger relative to the pattern. More specifically, the inventioncomprises an electric pickup type of tracer which is adapted to producean error signal whenever the tracer deviates from the pattern outline.This signal is then utilized to control the hydraulic actuators of themachine and return the tracer to the pattern outline. The tracer controlmechanism may be applied to any desired type of reproducing apparatuswhich is designed for hydraulic operation. For example, it may be usedto control the operation of an automatic profiling machine in which oneor more pieces of work are simultaneously contoured to conform to theoutline of a master templet or pattern. The form of apparatusconstituting the present invention provides certain advantages over theprior art forms of tracer mechanisms and has been designed with a viewto enabling rapid and efficient reproduction of the master in theworkpieces. This is made possible by the use of electrical controlswhich provide rapid and accurate response to changes in direction of thepattern outline and to apply these controls to the electrohydraulicdevices which in turn control the hydraulic actuators of the machine.

In general, the present invention comprises a tracing finger which ismounted for rotation about its longitudinal axis so as to permit the useof eccentricity or anticipation in the system, and also for rotationabout a lateral axis so as to permit sidewise deflection of the fingerby the pattern. The sidewise deflection of the finger operates anelectrical pickup of the differential transformer type which produces anull signal when the tracer is following the pattern outline and anerror signal when the tracer departs therefrom. The phase of the errorsignal is indicative of. the overdeflection and underdefiection of thefinger by the pattern. This signal is fed into a discriminator circuitand rectified so as to produce a direct current voltage whose polarityis dependent on the phase of the a error signal. This voltage is thenamplified and utilized to control the engagement of a pair of magneticclutches which afford a reversible drive to the gear which rotates thefinger about its longitudinal axis. This gear carries a sine-cosine camwhich adjusts the armatures of a pair of variable difierentialtransformers which are spaced 90 degrees apart around the cam; Hence,the voltage produced by one transformer will vary as the sine of theangular displacement of the cam while the other voltage will vary as thecosine thereof. These voltages are amplified with care being taken tomaintain the linearity of the voltages throughout the various circuitsso as to preserve the sine-cosine relationship between the voltages. Theamplified voltages are then applied to thg servo mo tors which in turncontrol the displacement of a pair of variable displacement pumps whichcontrol the rate and direction of movement of the hydraulicallyoperated, transversely movable slides of the machine. Since the vectorsum of the sine and cosine components always remains the same regardlessof the position of the cam which turns with the tracing finger, andsince the response of the system to and including the variabledisplacement pumps is'linear, the feedrate of the cutting tool of themachine, and also of the tracer, will remain the same in all directionsof travel. The correction applied by the error signal to the rotationalposition of the cam and finger is always such as to reduce the over orunderdellection of the tracing finger thereby causing the tracer tofollow the direction of the pattern outline. Likewise, the rotationalposition of the finger and cam are always indicative of the direction oftravel of the cutting tool and tracing finger relative to the work andto the pattern.

Means is also provided for reducing the magnitude of the sine and cosinevoltages when the error signal exceeds a predetermined value so as toreduce the feed rate of the cutter when sudden changes in direction areencountered such as, for example, a right-angle corner on the pattern.This reduction of the magnitude of the sine and cosine voltages willreduce the error which would otherwise occur under such circumstancesdue to the inability of the machine to respond with sutficient rapidityto abrupt changes in direction of the pattern outline.

A variable speed drive is also provided for the variable displacementpump-s so that the feed rate of the machine may be adjusted to suit therequirements of the work by simply increasing or decreasing the speed ofthe pumps. This is a decidedly advantageous feature inasmuch as iteliminates the low feed rate errors which normally are present inconventional forms of tracer mechanisms. It has been common practice inprior constructions to control the feed rate by varying the magnitude ofdisplacement of the sine-cosine cam or other displacement producingmeans, the magnitude being reduced when a reduced feed rate is desired;This reduction of magnitude, however, greatly increases the criticalnessof re sponse of the devices controlled by the .cam since the movement ofthese devices becomes very small in relation to the rotational movementof the cam. Hence, errors are introduced into the tracing system by theinability of the devices controlled by the cam to respond withsufiicient accuracy to small rotational movements of the cam to effectthe necessary control of the operating mechanism of the machine. With asystem employing variable displacement pumps, the same difficulty isencountered when an attempt is made to reduce the displacement of thepumps in order to achieve reduced feed rates. By so doing, the pumps areoperated around their positions of zero displacement so that theinherent mechanical errors become a greater proportion of the totaldisplacement'and are, in effect, magnified and prevent accurateoperation of the tracing system at low feed rates. However, with thepresent system of reducing the speed of the pumps, these difficultiesare avoided and the system operates with the same accuracy at low feedrates as it does at high feed rates from the standpoint of the accuracyof thepic'kups, servos, and pumps. Hence, the criticalness of thecomponents of the system is avoided and the construction of the tracercontrol mechanism is simpli fied and rendered less costly than in thecase of previous forms of construction. l

Accordingly, it is an object of the present invention to provide atracer control mechanism incorporating new and improved features ofconstruction and modes of operation. 7

Another object of the invention'is to provide a new type of tracercontrol mechanism for machine tools which utilizes an electric tracinghead for producing electric signals to control a pair of variabledisplacement pumps which drive the hydraulic actuators of the machine.

Another object of the invention is to provide a novel means for causingthe feed rate of the cutting tool to be automatically reduced whensudden changes of direction in the pattern outline are encountered.

Another object of the invention is to provide a hydraulically operatedmachine tool in which variable displacement pumps are utilized forcontrolling the rate and direction of travel of the cutting tool andwhich in turn are controlled by electric signals produced by the tracinghead after being analyzed and amplified by control circuits which aredesigned to provide a linear response to the signals.

With these and other objects in view which will become apparent from thefollowing description, the invention includes certain novel features ofconstruction and combinations of parts the essential elements of whichare set forth in the appended claims and a preferred form or embodimentof which will hereinafter be described with reference to the drawingswhich accompany and form a part of this specification.

Referring to the drawings in which like reference numerals indicate likeor similar parts:

FIG. 1 is a front elevation of a milling machine to which is shownapplied the tracer mechanism constituting the present invention.

FIG. 2 is a diagrammatic view showing the manner in which the presentinvention is connected into the hydraulic system of the milling machine.

FIG. 3 is a cross-sectional elevation of the tracing head viewed fromthe front.

FIG. 4 is a perspective view of the eccentric adjustment for the tracingfinger.

FIG. 5 is a cross-sectional elevation of the tracing head taken alongthe line 5-5 in FIG. 6.

FIG. 6 is a horizontal cross-sectional view taken through the upper partof the tracing head.

FIG. 7 is a circuit diagram of a regulated power supply for delivering aconstant direct current voltage to the electrical control apparatus.

FIG. 8 is a circuit diagram of another regulated power supply fordelivering a constant direct current voltage to the electrical controlapparatus.

FIG. 9 is a circuit diagram of a control circuit for facilitating thechangeover from hand servo control to tracer control.

FIG. 10 is a circuit diagram of a portion of the electrical controlapparatus for the machine including the vacuum tube oscillator, and thethrottling circuit for effecting slow-down when a sharp corner isencountered.

FIG. 11 is a circuit diagram showing a portion of the rotation controlapparatus.

FIG. 12 is a circuit diagram of the electrical apparatus for controllingmovement of the table of the milling machine.

FIG. 13 is a circuit diagram of the electrical apparams for controllingmovement of the cross-slide of the milling machine.

FIG. 14 is a block diagram of the tracing system.

FIG. 15 is a schematic view of the variable displacement pumps and thecontrolling apparatus therefor.

Machine tool In the accompanying drawings the invention forming thesubject matter of the present application is shown as applied to ahydraulically actuated milling machine of a known type. It is to berealized, of course, that the inventive features of the tracer controlapparatus could be used with equally satisfactory results with othertypes of hydraulically actuated machine tools where it is desirable toprovide means for reproducing in a workpiece the shape of a master orpattern. The milling machine shown in FIG. 1 comprises a bed on which awork table 21 is mounted for longitudinal sliding movement.

Supported on the bed behind the table is a cross-slide 23 which ismounted for horizontal sliding movement on ways 24 in a fore and aftdirection, that is, at right angles to the direction of movement of thetable 21. A tool head 25 carrying a power driven spindle 26 and cutter27 is mounted for vertical sliding movement on the crossslide 23 so asto provide three dimensional movement of the cutter relative to aworkpiece 28 mounted on the table. On the right-hand side of the head 25is mounted a saddle 29 which is supported for horizontal slidingmovement in a fore and aft direction on the head by suitable ways 30.The saddle is provided with vertical ways on which a saddle 36 ismounted for vertical sliding movement. The saddle 36 is provided with ahorizontal arm 37 on which a tracing head slide 38 is mounted forhorizontal movement along the arm 37. A tracing head 39 is mounted onthe slide 38 so that a tracing finger 40 depending therefrom will movein unison with the cutter 27 and follow the contour of a pattern 41fastened to the table. Also, by virtue of the particular mounting of thetracing head 39 upon the tool head 25 just described, the tracing finger40 may be adjusted in any direction with respect to the cutter 27 forset up purposes.

The milling machine herein illustrated is of the same general type asthat shown in US. Patent No. 2,239,625 granted April 22, 1941 to ErwinG. Roehm and Hans Fritschi and, like the machine of that patent, isprovided with means for enabling hand operation of the table,cross-slide and head. For this purpose, a hand wheel 45 is mounted onthe front of the machine bed in a convenient position for manualoperation to effect traversing movement of the table 21 in one directionor the other depending upon the direction of rotation of the hand wheel.This movement of the table is effected hydraulically by a handservovalve, the plunger of which is moved in one direction or the otherin accordance with the direction of rotation of the hand wheel. Thevalve plunger is connected with the hand wheel 45 by means of suitablegearing and a half nut operating on a feed screw in the manner describedin the aforementioned patent. The cross-slide 23 may be caused to moveback and forth along the ways 24 in a similar manner by suitablemanipulation of a hand wheel 46 also mounted on the front of the machinebed 20. Likewise, vertical movement of the toolhead 25 may be effectedby manipulation of a hand wheel 47, or a hand wheel 48, which handwheels are geared together for a conjoint rotation. When the machine isunder control of the tracer, the hand servo controls are selectivelyrendered ineffective to prevent misoperation of the machine.

Hydraulic circuits The hydraulic actuators and the control apparatustherefor of the milling machine shown in FIG. 1 are illustrateddiagrammatically in FIG. 2 of the drawings. As therein shown, thehydraulic actuator of the table 21 comprises a hydraulic cylindercontaining a piston 56 mounted on a piston rod 57 which is bolted to thetable. The table may be moved in either direction by selectivelycontrolling the flow of fluid to the opposite ends of the cylinder 55.The cross-slide 23 is operated by a similar hydraulic actuatorconsisting of a cylinder 58, piston 59 and piston rod 60 bolted to thecross-slide. In a like manner, the tool head 25 may be caused to move upor down on the cross-slide by means of a hydraulic cylinder 61 securedto the head and containing a piston 62 mounted on a piston rod 63 whichis bolted to the cross-slide 23.

Hydraulic fluid under pressure is supplied to the abovementionedactuators by means of a pump 65 driven by a motor 64 which draws thefluid out of a sump 66 and delivers it under pressure to a system ofhigh pressure lines 67. Pressure in the lines 67 is maintained constantunder varying demands on the system by a pressure relief valve 68connected to the pressure side of pump 65 and havinga discharge line 69emptying into the sump 66.

The flow of high pressure fluid to the cylinders 55, 58 and 61 iscontrolled by hand servovalves 70, 71 and 72, respectively, when aselector valve 73 is set in the Hand position as shown in FIG. 2. Thevalve 73 includes a pair of valve plungers 74 and 75 which are connectedtogether for simultaneous operation by means of a centrally pivotedlever 76 to which the ends of the plungers are pivotally connected.Hence, when plunger 74 is moved to the left as viewed in FIG. 2 theplunger 75 will be moved to the right, and vice versa. With the selectorvalve 73 positioned as shown, the left-hand end of the cylinder 55 iscommunicatively connected with the n'ght hand motor port of valve 70 bylines 77 and 78. In a like manner, the right hand end of the cylinder 55is communicatively connected with the left-hand motor port of valve 70by lines 79 and 80. The center, or pressure port of the valve 70 is, ofcourse, connected to the system of high pressure lines 67 while theexhaust ports of the valve are connected to a system of drain lines 81through which the hydraulic fluid is returned to the sump 66.

In a like manner, the hand servovalve 71 for the crossslide cylinder 58will be effective to control the flow of fluid to and from itsassociated cylinder when the selector valve 73 is in the position shown.In this position of the valve, the left-hand end of cylinder 58 iscommunicatively connected with the right-hand motor port of valve 71 bylines 82 and 83. Likewise, the right-hand end of the cylinder isconnected to the left-hand motor port by lines 84 and 85. The center, orpressure port of the valve is connected to the high pressure line 67 andthe exhaust ports are connected to the drain line 81.

The hand servovalve 72 is effective to control the flow of hydraulicfluid to and from the head cylinder 61 by means of line 86 whichconnects the upper end of the cylinder to the bottom motor port of thevalve and a line 87 which connects the lower end of the cylinder to thetop motor port of the valve. The center port of the valve is connectedto the high pressure line 67 and the exhaust ports thereof are connectedto the drain line 81.

From the foregoing it will be clear that when the machine is set forhand operation, each of the hand servovalves 70, 71 and 72 will berendered effective to control the flow of fluid under pressure to andfrom the cylinders of the hydraulic actuators. The direction of movementof the pistons within the cylinders will be dependent upon the directionof movement of the plungers of the valves which, in hand operation ofthe machine, is effected by hand wheels 45, 46, 47 and 48 (FIG. 1) whichare connected through gearing with half nuts moving with the valveplungers. This mechanism is fully described in the previously mentionedUS. Patent No. 2,239,625 and need not be described in detail hereinexcept insofar as is necessary for an understanding of the manner inwhich the changeover is eflected from hand servo control to tracercontrol.

Referring again to FIG. 2, the plunger of the hand servovalve 70 isbored to slidably receive a feed screw 90 which is bolted to the table21. As diagrammatically illustrated herein, the feed screw 90 is adaptedto be engaged by a half nut 91 which is carried by and moves with theplunger of the valve and is pivoted thereto for movement into or out ofengagement with the feed screw 90. As described in the aforementionedpatent, the plunger and half nut may be rotated by means of a gear 92connected to the hand wheel 45 for rotation-thereby. Hence, with thehalf nut engaged with the feed screw 90, rotation of the plunger andhalf nut will cause the plunger to be fed along the screw therebyadmitting fluid under pressure to one end of the cylinder 55 andconnecting the other end of the cylinder to drain. The resultingmovement of the piston 56 will cause movement of the table 2.1 which inturn will center the plunger of the valve to stop further movement ofthe table, the body of the valve being fast on the bed of the machine.When the half nut is disengaged from the feed screw, however,

the table will then be free to move with reference to the is constructedand arranged in the same manner as the valve 70 just described. That is,the plunger of the valve is bored to slidably receive a feed screw 95which is bolted to the cross-slide and adapted to be engaged by a halfnut 96 pivotally supported on the plunger of the valve. Rotation of theplunger and half nut may be efiected by manipulation of the hand wheel46 (FIG. 1) which is connected by suitable gearing with a gear 97rotating with the plunger. Hence, the cross-slide may be moved back andforth under power by suitable manipulation of the hand wheel 46 which,when the half nut 96 is engaged, causes feeding movement of the plungerof the valve along the feed screw and produces corresponding movement ofthe cross-slide while the hand wheel is being turned.

The servovalve 72 for the head cylinder 61 is similarly constructed. Theplunger of this valve is bored to slidably receive a feed screw 100which is adapted to be engaged by a half nut 101 pivotally supported onthe valve plunger. Rotation of the plunger and half nut by the handwheels 47 and 48 (FIG. 1) is effected bya suitable drive from the handwheels to a gear 102 which rotates with the plunger of the valve.Therefore, with the half nut engaged, rotation of the hand wheels willcause feeding movement of the plunger along the feed screw and causecorrespondingmovement of the cylinder 61 relative to the cross-slide 23.For reasons later to be explained, the plunger of the valve 72 is biasedupwa-rdly by a spring 103 compressed between an offset in the valve bodyand a flange formed on the valve plunger. So long as the half nut 101 isengaged with the feed screw 100, however, the spring 103 is ineffectiveto move the valve plunger out of its centered position.

Each of the half nuts 91, 96 and 101, is normally biased into engagementwith its related feed screw but may be disengaged therefrom upon theapplication of hydraulic pressure to a small hydraulic actuatorassociated with each half nut. As shown in FIG. 2, the hydraulicactuators for the half nuts 91 and 96 are connected by a line 105 with aport on the selector valve 73. This port is connected with the drainline 81 when the plunger 75 of the valve is in the position shown inFIG. 2. Hence, when the selector valve is set for hand servo operation,the half nuts will be engaged with their related feed screws. When,however, the valve 73 is shifted to Tracer position, a port on theselector valve connected with high pressure line 67 will becommunicatively connected with the line 105 to thereby supply pressureto the actuators for the half nuts 91 and 96 and remove these half nutsfrom the feed screws 90 and 95. This will cause the valves 70 and 71 forthe table and cross-slide to be conditioned for a tracer operation bydisassociating the valve plungers from their associated feed screws soas to permit the feed screws to move within the plungers without anyinterference thereby during operation of the machine under the controlof the tracer.

The hydraulic actuator for the half nut 101 is connected bya line 106with a port on a solenoid valve 107.

head 25. When the machine is set fortracer control, the.

same condition prevails with respect to the hand servovalve 72, i.e.,the half nut 101 remains engaged with the feed screw 100 under normalconditions of operation under tracer control. This permits raising andlowering of the tool head 25 under control of hand wheels 47 and 48during tracer control in the same manner as whenthe machine is set forhand servo operation.

'7 Tracing head When the machine heretofore described is to be used forthe automatic reproduction of a master or pattern, it is placed underthe control of the tracing head 39, the tracing finger 40 of which isadapted to contact the edge of the pattern 41 and to follow the outlineof the pattern as the tracing operation proceeds. As shown in FIGS. 3,4, 5 and 6 of the drawings, the tracing head 39 is mounted in a casingwhich is in the form of .a hollow box having removable top and sidepanels which aflord access to the interior of the head. In the bottom ofthe casing there is provided a circular opening for receiving the upperend of a cylindrical housing 111 which is secured to the casing 110 byfastening screws 112. Rotatably journaled within the housing 111 is asleeve 113 within which the stem 114 of the tracing finger 40 is housed.As shown in FIG. 3, the sleeve 113 is journaled for rotation within thehousing 111 by an upper set of ball bearings 117 and a lower set ofroller bearings 118. The ball bearings 117 are retained within a recessprovided in the upper end of the housing 111 by a retaining ring 119which is held in place on the upper end of the housing by suitablefastening screws. The roller bearings 118 are retained within a recessprovided in the lower end of the housing by a bottom cap 120 which isfastened to the bottom of the housing by screws 121. The sleeve 113 isprovided toward its lower end with a taper 122 which is adapted toengage a similar taper formed on the inner race of the roller bearing118, the taper 122 being seated therein and held thus engaged by a drawnut 123 meshing with a screw thread 124 provided on the sleeve justabove the taper 122. The interior of the housing 111 is sealed againstthe entrance of dust and dirt by a ring or gasket 125 of syntheticrubber or similar material which also serves as an oil seal between thelower end of the housing and the sleeve 113.

Near its lower end, the stem 114 is provided with a spherical prominencewhich seats in a counterbore formed in the lower end of a pivot ring 131which is securely fastened to the bottom of the sleeve 113 by a ball 132forced into a V-shaped groove in the sleeve by a set screw 133 in thering and a locating pin 134 in the ring which projects into a groove 135formed in the sleeve. The stem 114 is constrained to rotate with thesleeve 113 due to the engagement of the inner end of a pin 136 in thering engaging with a groove 137 formed in the ball pivot 130. Rotationof the sleeve and stem is effected by means of a spur gear 140 mountedupon and keyed to the upper end of the sleeve 113. If desired, a degreescale may be inscribed on the peripheral face 141 of the ring 131 sothat the angular position of the tracing finger with relation to thehousing 111 of the tracing head may be determined by reading the scaleagainst an index line inscribed on the peripheral face 142 of the cap129. Also, a portion of the face 141 is preferably knurled so as tofacilitate turning the ring 131 by hand for a purpose later to bedescribed.

Eccentricity of the lower end of the tracing finger 40 with respect tothe axis of rotation of the sleeve 113 is provided for by a coupler 145which serves to connect a cylindrical contact element 146 of the tracingfinger with a shank 147 formed on the bottom of the stem 114. Thecoupler 145 includes a top slide 148, a bottom slide 149 and a crossblock 150. The cross block is provided on its upper surface with afeather 151 which is slidable within a groove 152 formed in the upperslide 148. The b ock 151 is provided on its lower surface with a feather153 lying at right angles to the feather 151 and slidably receivedwithin a groove 154 in the bottom slide 149. The assembly is heldtogether by longitudinally extending screws 161.

The block is provided with an upper pair of oppositely disposedadjustment screws 155 adapted. to bear against opposite sides of theshank 147 and also with a lower pair of adjustment screws 156 disposedat right angles to the screws 155 and adapted to bear against oppositesides of a dowel pin 157 mounted in the bottom slide 149. Also carriedby the slide 149 is a pin 160 on the lower end of which the contactelement 146 is fastened. The pin is secured to the bottom slide 149 by aset screw 158 and the upper slide 148 is secured to the shank 147 by apin 159. Hence, by suitable adjustment of the screws 155 and 156, thecontact element 146 may be offset in any direction from the central axisof the stem 114 so that eccentricity may be introduced in any desireddirection.

As is well known in the art, it is desirable to offset the contactelement in the direction of tracing so as to provide a certain amount ofanticipation to compensate for the time lag in the response of thesystem to changes in direction of the pattern. Eccentricity of thecontact element with respect to its axis of rotation also introduces acertain amount of feed back into the system since it tends to reduce theerror signal in response to the applied correction. This, as is wellknown, tends to increase the stability of operation of the system.

Sidewise deflection of the element 145 by the edge of the pattern 41 istranslated into vertical movement of a plunger slidably mounted within abushing 166 inserted in the upper end of the sleeve 113 by means of aball 167 which seats in conical recesses provided in the top and bottomof the stem 114 and plunger 165, respectively. The upper end of theplunger 165 bears against the bottom of a lever 163 which is pivoted at169 between a pair of brackets 176 secured to the bottom face of alaminated phenolic body 171 supported on the bottom of the casing 110 bythree posts 172. As shown in FIG. 3, the left-hand end of the lever 168lies beneath the lower end of a plunger 173 of a linear variabledifferential transformer 174 which includes a primary winding 175, apair of secondary windings 176 and a magnetic core 177 carried by theplunger 173 for axial movement relative to the primary and secondarywindings of the transformer. The plunger 173 is journaled for slidingmovement in upper and lower threaded plugs 178 and 179, respectively,which retain the windings of the transformer in position within the boreinto which the plugs are screwed. A compression spring 180 compressedbetween the bottom of a bore in the plug 179 and an abutment flange onthe plunger 173 urges the bottom end of the plunger into contact withthe top edge of the lever 168.

A predetermined amount of downward pressure may be applied to theplunger 165 by means of a spring pressed plunger which is slidablymounted within an externally threaded sleeve 186 which screws into athreaded hole provided in the body 171. The plunger 185 is located inaxial alignment with the plunger 165 and is pressed downwardly by aspring 187 which is compressed between the top of the plunger 185 andthe lower end of a screw 183 which screws into the upper end of thesleeve 186. Screw 183 is provided with a knurled head 189 whereby thescrew may be turned to adjust the compressive force of the spring 187against the plunger 186 so that a predetermined sidcwise force must beapplied to the contact element 146 to produce deflection of the stem 114and elevation of the plunger 173 of the differential transformer 174.

As will be more fully explained hereinafter, the differentialtransformer 174 operates to produce an electric signal which mayappropriately be referred to as an error signal whenever the tracingfinger 4t) departs from its position of normal deflection. The tracinghead 39 is provided with two additional linear variable differentialtransformers and 196 (FIG. 6) which will hereinafter be referred to asthe sine and cosine transformers or pickups since they are so arrangedas to produce a pair of A.C. voltages whose amplitudes vary as the sineand cosine functions of the rotational position of the tracing finger40, and whose phase shift is determined by the algebraic sign of thesine-cosine functions. As will be observed from FIG. 6, the lastmentioned transformers are so mounted in the body 171 as to lie 90degrees apart about the central axis of the rotatable sleeve 113. Thetransformers 195 and 196 are provided with plungers 197 and 198,respectively, which hear at their lower ends against a sine-cosine cam199 (FIG. formed on the upper face of the gear 140. The cam 199 is soshaped as to provide a vertical displacement of the plungers 127 and 198which varies as the sine and cosine functions of the angular position ofthe gear 140.

Inasmuch as the transformers 195 and 196 are of identical construction,it will be necessary to show and describe only one of them for acomplete understanding of the invention. As shown in FIG. 5, thetransformer 195 includes a primary winding 205 and a pair of secondarywindings 266 which windings are of cylindrcal form and are receivedwithin a bore within which they are retained by upper and lower threadedplugs 267 and 208, respectively. ,The plugs are centrally apertured toreceive the plunger 157 and serve to guide the plunger for axialmovement relative to the windings. The plunger carries a magnetic core269 which may be moved by the plunger in one direction or another from acentered or null position. A light compression spring 210 surrounds thelower end of the plunger 197 and urges the plunger downwardly againstthe face of'the cam 199. The purpose and mode of operation of thesine-cosine transformers will be described in a later portion of thespecification.

The rotational position of the tracing finger 48 is effected through thegear 140 by means of a pair of magnetic clutches 215 and 216 (FIG. 5)which are located with-in the casing 110 of the tracing head. Power isprovided for driving the clutches by an electric motor 222 supported onthe plate 38 (FIG. 1) which drives a shaft 223 through suitablereduction gearing 224 and a drive coupling 225. The shaft 223 issupported for rotation within a cylindrical housing 226, mounted on onecorner of the casing 110, by means of upper and lower ball bearings 227and 228 which are retained and enclosed by upper and lower bearing caps229 and 239, respectively. The shaft 223 carries a pinion gear 234 whichis pinned or otherwise keyed to the shaft and which drives a pair ofmeshing spur gears 235 and 236 journaled for rotation on shafts 217 and218, respectively, which in turn are journaled for rotation in thecasing 118 by ball bearings 221.

As shown by the cross-sectional representation of the clutch 216, eachof the magnetic clutches includes a floating armature disc 237, a rotor238 and a stationary field coil 239. The floating armature disc 237 isconstrained to rotate with the driving gear 236 while being free to movethrough a limited distance axially of the gear. The rotor 238 is rigidlysecured to the shaft 218 and forms a part of the magnetic circuitcreated by the stationary field coil 239 when the latter is energized.The field coil 239 is enclosed in a housing 242 which is journaled by abushing 241 on a sleeve 248 formed integrally with the rotor 238. Themagnetic clutches 215 and 216 are of a commercially available type andthe detailed features of construction thereof are not important insofaras the present invention is concerned.

Engagement of each of the clutches is effected by energization of itsfield coil 239 which sets up a magnetic flux through the rotor andarmature disc of the clutch which attracts the armature disc to therotor and causes the mating faces 243 thereof to be frictionally engagedthereby causing the rotor to be driven by the driving gear. Keyed to theshafts 217 and 218 are spur gears 247 and 248 each of which meshes withthe spur gear 1 .8 (FIG. 6). Since the driving gears 235 and 236 arerotated in opposite directions, the gear 140 will be driven full-waverectifier tube 258.

D.C. power supplies The electronic control equipment for the tracerwhich is shown in FIGS. 10, ll, 12 and 13, and which is housed in anelectrical cabinet 250 (FIG 1), requires a source of constant D.C.voltage in order to insure linear amplification and handling of thesignals supplied thereto by the differential transformers in the tracinghead. For this purpose, the regulated power supplies shown in FIGS. 7and 8 of the drawings are provided. The supply shown in FIG. 7 providesapproximately 300 volts D.C. at the plate voltage supply terminal 255while the supply shown in FIG. 8 isintended to provide a source ofapproximately 400 volts D.C. at the terminal 256 for the direct currentamplifier circuits of the control apparatus.

The power supply shown in FIG. 7 includes a power transformer 257 havinga primary winding adapted to be connected by terminals 253 to the powerline, and a centertapped secondary winding for operating the plates of aIn order to provide a delay to allow the filaments of the vacuum tubesof the electronic circuits to heat up before plate voltage is appliedthereto, a thermostatic type delay relay 259 has its heater connected inparallel with the primary winding of the transformer so as to cause thenormally open contacts 254 of the relay to close at a predetermined timeafter energization of the primary winding of the transformer. Contacts254 control the energization of a relay coil 260, the forward contacts261 of which are inserted in the line connecting the center tap of thesecondary winding to ground. Therefore, voltage cannot be supplied bythe transformer and rectifier tube to the terminal 255 until thecontacts 254 are closedafter a predetermined time delay.

The rectified A.C. voltage furnished by the tube 258 is filtered bychoke 262, condenser 263 and load resistor 264. The output from thefilter is applied to the output terminal 255 through a regulator tube265 which is of a low mu, twin triode design intended for D.C. amplifierservice. The two sections of the tube are connected in parallel toincrease the current handling capacity of the tube. The grid bias of thetube 265 is determined by the voltage on the plate' of a twin triodecontrol tube 266. The voltage on the cathode of the left-hand section-ofthe tube is stabilized by a voltage regulator tube 267 while the voltageon the grid of this section is determined by the voltage on the plate ofthe right-hand section of the tube. The cathode of the right-handsection is connected to a tap on a voltage divider connected in seriesbetween the output terminal 255 and ground, and the voltage on the gridof this section of the tube is maintained constant inasmuch as it issupplied from a tap on a voltage divider connected across the voltageregulator 267. Hence, any change in voltage at the output terminal 255will result in a change of voltage on the cathode of the right-handsection of tube 266 thereby changing the bias on this section of thetube and varying the plate voltage which changes the bias on theleft-hand section of the tube. This varies the voltage on the left-handplate thereby adjusting the 11 which, when energized, closes relaycontacts 274 connected between the center tap of the secondary windingand ground. Therefore, no voltage will be supplied to the terminal 256until the coil 273 is energized after a predetermined interval followingenergization of the primary winding of the transformer.

The rectified output from the tubes 271 is filtered by choke 275,condenser 276 and resistor 277 and the filtered output is supplied tooutput terminal 256 through a plurality of parallel-connected regulatortubes 278. The voltage drop across tubes 278 is controlled by twintriode tube 279 in which the voltage on the cathode of the lefthandsection and on the grid of the right-hand section are stabilized by thevoltage regulator tube 280. The voltage regulator circuit includingtubes 278, 279 and 280 operates in the same manner as the voltageregulator shown and described in FIG. 7 to control the voltage at theoutput terminal 256 and to maintain it constant under varying conditionsof load.

Alternating current generator To eliminate stray pickup and to providefast response by the rotation control system of the tracer, the differemtial transformers 174, 195 and 196 (FIG. 6) of the tracing head aresupplied with an energizing voltage of approximately 10,000 cycles persecond provided by a local AC. voltage generator. This generator, which,in the present embodiment, comprises a vacuum tube oscillator of theWein-bridge type, illustrated in the upper left-hand corner of FIG. ofthe drawings. The oscillator includes a twin triode type vacuum tube 285the output from the left-hand section of which is inverted and amplifiedby the right-hand section of the tube. The output of the right-handsection is fed back to the input of the left-hand section of the tubethrough a coupling condenser 286. The feedback voltage is passed througha frequency discriminating network including seriesconnected condenser287 and resistor 288, and parallelconnected resistor 289 and condenser290. The values of these components are so chosen as to favor afrequency of 10,000 cycles per second and thereby cause the circuit tooscillate at that frequency. A degenerative feedback voltage is appliedto the left-hand section of the tube 285 by a voltage divider consistingof the filament of a lamp 291, a resistor 292 and a variable resistor293. The amount of negative feedback may be controlled by manipulationof the resistor 293 so as to maintain the amplitude of output from theleft-hand section of the tube at a low enough level to insure that thewave form will be approximately sinusoidal. The 300 volt power supply ofFIG. 7 provides a constant voltage source for operating the oscillator,the plates of the tube 285 being connected to the output terminal 255 ofthis power supply.

The 10,000 cycle voltage from the oscillator is taken from the cathodeof the right-hand section of tube 285 and applied through a line 295 tothe grid of the lefthand section of a twin triode vacuum tube 296 theplates of which are supplied from the supply terminal 255. The left-handsection of the tube 296 is connected in a cathode follower arrangementwith the input of the righthand section through a band pass filter toimprove the wave form of the 10,000 cycle voltage. This filter includesseries connected resistors 297 and capacitors 298, and parallelconnected resistors 299 and capacitors 300 together with parallelconnected inductances 301. The filter is designed to discriminateagainst frequencies above and below 10,000 cycles per second so as tofurnish a pure 10,000 cycle signal to the grid of the right-hand sectionof tube 296. The right-hand section of the tube operates as a phaseinverter, the signal being taken from the cathode and plate thereof anddelivered through lines 303 and 304 and coupling condensers 305 and 306to the grids of a push-pull amplifier tube 302.

Rotation control circuit The plates of the tube 302 are supplied fromthe regulated voltage supply of FIG. 7 through a load resistor 308 andthe center tap of a primary winding of transformer 307. The secondarywinding of the transformer is connected in series with the primarywinding of the differential transformer or pickup 174 (FIG. 3) so as toenergize this winding with 10,000 cycle voltage. As shown in FIG. 10,the secondary windings 176 of the transformer 174 are connected in phaseopposition between ground and an output lead 309 which is connectedthrough a coupling condenser 310 to the grid of an amplifier tube 311.If desired, the connection between secondary windings 176 may beconnected to the slider of a potentiometer 312 connected across theouter ends of the windings so as to enable the balance point voltage ofthe transformer to be adjusted to a minimum value in a known manner.

When the tracing finger 40 is deflected sufiiciently from the verticalposition as shown in FIG. 3 to rock the lever 168 about its pivot 169and elevate the core 177 of the transformer to its centered or nullposition, a zero signal will be delivered to the grid of tube 311.However, if the tracing finger 40 is underdefiected or ovcrdefiectcd, a10,000 cycle signal will be delivered to the tube through the outputlead 309 due to the unbalance of the bucking voltages in the secondarywindings 176. The phase of the error signal voltage will shift through180 degrees at the null or balance point of the transformer due to thephase opposition of the voltages induced in the secondary windings 176.Hence the error signal produced by an overdefiection of the tracingfinger will be 180 degrees out of phase with the error signal producedby an underdefiection of the finger. Also, the amplitude of the errorsignal will, by virtue of the linear characteristic of the transformer174, be directly proportional to the extent of displacement of thefinger from its position of normal displacement.

The 10,000 cycle error signal delivered to the grid of the tube 311 fromthe transformer 174 is amplified and delivered through a potentiometer316 to a line 317 which is connected to the grid of a phase invertertube 315 (FIG. 11). The plate and cathode of the tube 315 are connectedthrough condensers 318 and 319, respectively, with the grids of a twintriode vacuum tube 320 whose plates are fed from the supply terminal 255through the center-tapped primary winding of a transformer 32!. The tube320 is connected in a conventional push-pull arrangement and theamplified 10,000 cycle error signal appearing in the plate circuit ofthe tube is fed into a discriminator circuit Which includes the centertapped secondary winding of the transformer 321 and a pair of seriesconnected potentiometers 322 and 323 Whose sliders are ganged forconjoint movement as indicated by dotted line 324. The potentiometersprovide a sensitivity control, the sliders moving in unison toward thepoint of connection between the two potentiometer Windings for thepurpose of decreasing sensitivity, and toward the outer or high ends ofthe windings for increased sensitivity.

The phase of the error signal fed to the discriminator by the vacuumtube 320 is compared with the phase of the amplified signal from theWien-bridge oscillator appearing on the bottom plate of the tube 302(FIG. 10) which is fed through a line 325 into the center tap of thesecondary winding of transformer 321 by a small coupling condenser 326and a pair of voltage dividing resistors 327 and 328 connected betweenthe condenser and ground which adjust the amplitude and phase of thereference voltage with respect to the phase and maximum amplitude of theerror signal. The sliders of potentiometers 322 and 323 are directlycoupled to the grids of a twin triode vacuum tube 330 in which bias isprovided by a cathode biasing resistor and in which the plates aresupplied with a source of positive voltage provided by the terminal 255through suitable load resistors. Consequently, the voltage applied toone of the grids of the tube 330 will be the sum of the error signalvoltage and the reference voltage from the signal generator while thevoltage appearing on the other grid of the tube will be the differenceof these voltages so that the two halves of the tube will conductunequally when an error signal is present. Of course, if thedifferential transformer 174 is in its null position, the voltages onthe grids of tube 330 will be equal so that both sections of the tubeconduct equally.

The plates of tube 330 are connected by coupling condensers 331 and 332to the plates of a twin diode tube 333 where the voltages from the twosections of the tube 330 are rectified and passed directly to the gridsof a twin triode D.C. amplifier tube 334. The tube 334 is provided witha cathode biasing resistor 3350f substantial value and the grids of thetube are provided with a positive bias by a voltage divider comprised ofresistors 336 and 337 connected in series between supply terminal 255and ground, the grids being connected to the junction between theresistors through suitable grid resistors The plates of tube 334 areconnected to the grids of a pair of DC. power amplifier tubes 351 and352 through a derivative damping network comprised of resistors 346,

347 and 348 and condensers 349 and 350. The plates of the tubes 351 and352 are connected with the supply terminal 256 (FIG. 8) through areversing switch 355, the energizing coils 239 (FIG. of the clutches 215and 216, normally open relay contacts 3581 controlled by a relay 358(FIG. 9), and a resistor 359. A source of stabilized DC. voltage isprovided for the screen grids of tubes 351 and 352 by means of a pair ofseries connected voltage regulator tubes 362 and 363, and the bias ontubes 351 and 352 may be adjusted by means of a rheostat 366 connectedin series with a cathode biasing resistor 367 which is common to bothtubes. When the machine is conditioned for hand servo control, theplates of tube 334 and the grids of tubes 351 and 352 are grounded bytwo pairs of normally closed contacts 3582 and 3583 controlled by therelay 358 (FIG. 9).

The derivative damping network comprised of resistors 346, 347 and 348,and condensers 349 and 350, operates as follows: When the tracing finger40 is in its null position, both sections of twin triode tube 334 willconduct equally so that the voltages on the plates will be equal, theload resistors in the two plate circuits being of equal value. If now,the tracing finger undergoes a large deflection due to an abrupt changein the pattern outline, a potential difierence will suddenly appearbet-ween the plates of the tube 334, one plate becoming more positivewhile the other plate becomes more negative. Which plates becomes morepositive and which more negative depends, of course, on whether thetracing finger is overdei'lected or underdefiected. The machine beingunder tracer control, the contacts 3582 and 3583 are now open and theresistors 346, 347 and 348 are effectively in series between the platesof tube 334 with the grids of tubes 351 and 352 connected across theresistor 347. The sudden voltage impulse developed between the plates oftube 334 will appear instantaneously across the resistor 347 due to theinability of condensers 349 and 350 to charge instantaneously. This willcause a large difierence in potential to appear between the grids oftubes 351 and 352 and a correspondingly large difference in the amountof current flowing through the coils 239 of the clutches. Hence, a largetorque will be applied by the clutches to the gear 140 to accelerate thetracing finger rapidly in whichever direction is necessary to reduce thedeflection of the finger caused by the pattern. The condensers 349 and350 will then charge and cause a voltage drop to occur across resistors346 and 348 and reduce the voltage drop across resistor 347 and the 14voltage between the grids of. tubes 351 and 352. This reduces thedifference in current flow between the coils 239 and causes acorresponding reduction in the torque on gear 140. After a sufficientperiod of time, depending upon the time constant of the chargingcircuits of the condensers 349 and 350, the voltage between the plateswill divide normally among the three resistors and the torqueon gearwill become constant. It will be appreciated, of course, that when zeroerror signal is present, the tubes 351 and 352 will conduct equally sothat the magnetic clutches 215 and 216 (FIG. 5) will be in balance andno rotation of gear 140 will occur.

The purpose of contacts 3581 (FIG. 11) is to break the plate circuit oftubes 351 and 352 when the relay 358 (FIG. 9) is de-energized andthereby deactivate the clutches 215 and 216 so that thering 131 (FIG. 3)can be turned. by hand. At the same time, the contacts 358- 2 and358'--3 will be closed thereby grounding the grids of tubes 351 and 352so as to prevent excessive screen current from flowing through the tubeswhile the plates are cut off.

The control apparatus just described for effecting rotation of thetracing finger in response to an error signal created by overdeflectionor underdeflection of the finger may appropriately be referred to as therotation control since it functions to maintain the direction ofeccentricity of the tracing finger tangent to the contour of thepattern. By means which will now be described, the relative movement ofthe table and cross-slide is controlled by the angular position of thetracing finger so as to cause the finger to move relative to thepattern, and the cutter to move relative to the workpiece, in thedirection of the eccentricity of the tracing finger. The basic directionof tracing may be reversed by operating the reversing switch 355 mountedon the front of the head 39 (FIG. 1), which reverses the direction ofcorrection applied to the tracing finger by the magnetic clutches.

Table control circuit As was mentioned earlier in the description, apair of sine-cosine transformers or pickups and 196 is arranged in thetracing head 39 for co-operation with the contour of a sine-cosine cam199 fashioned on the upper face of the gear 140. The transformer orpickup 196 controls the movement of the table 21 of the machine whilethe transformer or pickup 195 controls the movement of the cross-slide23.

Referring to FIG. 10, a potentiometer 375 is connected in the cathodecircuit of the right-hand section of tube 296. Theslider of thispotentiometer is connected through a condenser 376 with the grid of athrottle tube 377. The arrangement and functioning of this tube in thecircuit will be fully described at a later point in this specificationand for the present it will be sufficient to state that the plate of thetube is connected by a condenser 378 to ground through a potentiometer379 Whose slider is connected with the grid of a phase inverter tube380. The plate and cathode of this tube are connected through couplingcondensers with the grids of a push-pull amplifier tube 381 whose platesare fed from the supply terminal 255 through a dropping resistor and acenter tap on the primary winding of a transformer 382. Hence, the10,000 cycle voltage generated by the Wien-bridge oscillator will bedelivered to the secondary winding of transformer 382 one end of whichis connected to ground and the other end of which is connected by a line383 (FIG. 12) to one end of the primary winding 384 of the differentialtransformer 196. The other end of the primary winding is connected toground so that a 10,000 cycle energizing voltage will be supplied to theprimary winding of the transformer. The transformer 196 is'provided witha magnetic core 385 and with a pair of secondary windings 386 connectedin phase opposition in the same manner as the cross-slide transformer195 (FIG. 5). One end of the combined secondary windings 386 isconnected to ground while the other end is connected to ground through apotentiometer 388. The slider of potentiometer 388 is connected to thegrid of a phase inverter tube 389 the plate and cathode of which areconnected to the grids of a push pull amplifier tube 390 throughsuitable coupling condensers. The plates of the tube 390 are fed fromthe supply terminal 255 through a center tap on the primary winding of atransformer 391. The center tapped secondary winding of the transformer391 is connected in push-pull with the grids of a discriminator tube 392whose plates are tied directly to the supply terminal 255. The phase ofthe 10,000 cycle voltage delivered by the differential transformer 196and appearing in the secondary winding of transformer 391 is comparedwith the phase of a reference voltage of the same frequency in the inputcircuit of discriminator tube 392. This reference voltage is derivedfrom a line 393 connected to one plate of amplifier tube 381 (FIG. andis applied to the center tap of the secondary Winding of transformer 391(FIG. 12) by a coupling condenser 394 which, together with a resistor399, suitably adjust the amplitude and phase of the reference voltagewith respect to the maximum amplitude and phase of the control voltage.The grid and cathode of each section of tube 392 is operated well aboveground potential by means of a pair of resistors 395 and 396 which areof considerably greater ohmic resistance than the biasing resistors 397and 393 of the tube. Discriminator tube 392 operates in essentially thesame manner as the previously described discriminator 330 (FIG. 11) tocause one section of the tube 392 to conduct more heavily than the otherdepending on the phase of the voltage delivered to the transformer 391by the differential transformer 196. If the magnetic core 395 of thetransformer is in its centered or null position, no signal will bedelivered thereby to the transformer 391 and the two sections of tube392 will conduct equally.

The cathodes of tube 392 are coupled by condensers to the plates of arectifier tube 402 the cathodes of which are coupled directly to thegrids of a D.C. pushpull amplifier tube 403. The grids and cathodes ofthe tube 403 are balanced to ground by suitable resistors and a sourceof A.C. dither voltage 404 is introduced onto the cathode of the tube bya transformer 405 whose primary winding is connected to the source 404and whose secondary winding is connected to the cathodes of the tube.The frequency of the voltage source 404 may be as desired and in thecase of the present apparatus is derived from a 110 volt, 60 cyclesource.

The plates of the DC. amplifier tube 403 are fed from the supplyterminal 256 through a balancing potentiometer 408 and a pair ofsuitable load resistors. The output of tube 403 is fed to a DC. poweramplifier 406. For this purpose, the plates or" tube 403 are directlycoupled to the grids of DC. power amplifier tubes 409 and 410 and alsoto the grids of parallel connected tubcs 411 and 412, which are of thesame'type as tubes 409 and 410. The plates of the power amplifier tubesare fed directly from the regulated voltage supply terminal 256 whilethe screen grids of the tubes are connected to the supply throughsuitable voltage dropping resistors. The cathodes of the tubes areconnected to ground through biasing resistors 413 and 414 and areadapted to provide energizing current for a solenoid 415 one end ofwhich is connected to the cathodes of tubes 409 and 411 and the otherend of which is connected to the cathodes of tubes 410 and 412 as shownin FIG. 12, Consequently, when the output voltage from the differentialtransformer 196 is zero, equal currents will flow through the two pairsof tubes 409, 411 and 410, 412 and zero current will flow through thecoil 415 since the resistances of 413 and 414 are equal. However, when asignal is supplied to the circuit from transformer 196, a current willflow through coil 415 in one direction or the other depending on thedirection 16 of displacement of the core 385 of the transformer from itscentered .or null position.

Cross-slide control circuit The cross-slide 23 of the machine shown inFIG. 1 is controlled by a circuit which is similar to the circuit justdescribed in connection with the table 21. As shown in FIG. 10, theplate of throttle tube 377 is connected by a line 420 with the grid of aphase inverter tube 421 the plate and cathode of which are connected tothe grids of a push-pull amplifier tube 422 by suitable couplingcondensers. The plates of the tube 422 are fed from the supply terminal255 through a dropping resistor and a center tap on the primary windingof a transformer 423. The secondary winding of the transformer has oneend connected to ground and the other end connected to a line 424 which,as shown in FIG. 13, is connected to one end of the primary winding 205of differential transformer 195, the other end of which winding isconnected to ground. The primary winding of thetransformer is therebysupplied with a source of 10,000 cycle energizing voltage from theWien-bridge oscillator. The secondary windings 206 of the transformerare as hereinbefore stated connected in phase opposition between groundand an output line 425 which is connected to ground through apotentiometer winding 426. The slider of the potentiometer is connectedto the grid of a phase inverter tube 427 the plate and cathode of whichare connected by coupling condensers with the grids of a push-pullamplifier tube 428. The plates of the tube 428 are fed from the supplyterminal 255 through the center tap of a primary winding of atransformer 429 having a secondary winding the ends of which areconnected to the grids of a discriminator tube 430. A 10,000 cyclereference voltage is delivered to the center tap of the secondarywinding of transformer 429 through a coupling condenser 431 and a line432 (FIG. 10) which is connected to one of the plates of the amplifiertube 422. The discriminator tube 430 is arranged and functions in thesame manner as the discriminator tube 392 (FIG. 12) of the table controlcircuit so as to cause one section of the tube to conduct a largersignal than the other section depending on the phase of the voltagedelivered to the transformer 429 by the differential transformer 195.

The plates of the tube 430 are connected through coupling condensers tothe plates of a rectifier tube 435 the cathodes of which are connecteddirectly to the grids of a DC. push-pull amplifier tube 436. The gridsand cathodes of the tube 436 are balanced to ground through suitableresistors provided for this purpose and a source of A.C. dither voltage437 is applied to the cathodes of the tube through a couplingtransformer 438. The plates of the tube 436 are fed from the supplyterminal 256 through a balancing potentiometer 439 and suitable loadresistors. The output of tube 436 is fed to a DC. power amplifier 434,the plates of the tube 436 being directly coupled to the grids of D.C.power amplifier tubes 440 and 441 and to the grids of parallel connectedpower amplifier tubes 442 and 443. The plates of the power amplifiertubes are connected directly to the supply terminal 256 while thecathodes thereof are connected to ground through biasing resistors 444and 445 of equal value. The power amplifier tubes serve to energize asolenoid 446 one end of which is connected to the cathodes of the tubes440 and 442 and the other end of which is connected to the cathode oftubes 441 and 443.

As in the case of the table control circuit, when the magnetic core 209of the differential transformer is in its centered or null position, azero signal will be delivered to the circuit and the solenoid 446 willremain unencrgized. When, however, a voltage is produced in the outputline 425 of the differential transformer, a

current will flow through the coil 446 in one direction or the otherdepending on the phase of the voltage de-. livered by the transformer195.

It will be noted that inasmuch as the differential transformers 195 and196 each have a linear characteristic, and since the table controlcircuit and the cross-slide control circuit each is designed to preservethe linear relation of the output voltage from its'related trans-Hydraulic tracer control As indicated diagrammatically in FIG. 2 and asshown in greater detail in FIG. 15, the solenoids 415 and 446 controlthe operation of servo motors 451 and 452, respectively, which in turncontrol the displacement of variable displacement pumps 453 and 454,respectively. Considering first the mechanism for controlling themovement of the table 21, it will be observed that a polarized armature455 associated with solenoid 415 is connected to the upper end ofplunger 456 of servovalve 457. This valve is mounted on a subframe 458which is preferably secured to the mainframe of the machine tool. Thepunger 456 works in a follow up sleeve 459 which in turn is slidablewithin the valve body and is ported to co-operate with the lands on theplunger 456 to valve'the' hydraulic fluid to and from a power cylinder'460. The cylinder contains a piston 461 mounted on the end of a pistonrod 462 which is pivotally connected to the yoke 463 of the variabledisplacement pump 453 for the table. The follow up sleeve 459 isconnected by a link 464 to an arm 465 iulcrumed at 466 on the frame 458.At its opposite end, the arm 465 is slotted to receive a headed pin 467mounted on the piston rod 462.

Referring to FIG. 2 of the drawings, 'a source of fluid under pressureis provided for actuating the power cylinder 460 by a reducing valve 470which receives high pressure fluid from the high pressure line 67 andsupplies it at reduced pressure to a supply line 471 which is connectedto the center port of valve 457 (FIG. 15). The drain ports otthe valveare connected to the drain line 81 of the system and the motor ports areconnected by lines 472 and 473 to the ends of cylinder 460.

When the solenoid 4 15- is energized by a flow of current therethroughin one direction, the plunger 455 will be raised thereby raising theplunger 456 of the servovalve to cause fluid under pressure to flowthrough'line 473 into the lower end of cylinder 460 and raise the pistonand rotate the pump control arm 463 clockwise. Upward movement of thepiston -'rod 462 will raise the follow up sleeve 459 thereby centeringthe valve plunger with respect to the sleeve and cutting off the flow ofoil through the line 473. Conversely, when the current flow through thesolenoid 415 is in the opposite direction, the plunger 455 will bedepressed thereby lowering the valve plunger thus causing fluid underpressure tobe delivered to the upper end of the cylinder 460 throughline 472. This will move the piston downward and rock the yoke 463counterclockwise and lower the follow up sleeve 459 to. cut oil the flowof oil to the cylinder and prevent turther movement of the piston untilfurther movement of the valve plunger in either direction is effected.whereupon the piston 461 will again follow the valve plunger in itsmovements. Hence, there is provided a servo mechanism for operating theyoke 463 of the variable displacement pump 453 in accordance with theflow of.

current through the solenoid 415. In order tomaintain the linearity ofthe system, the solenoid must also have, a linear responseso thatmovement of the valve plunger will at all times be proportional to theamount of cur-- rent flowing through the coil 415.

The servo motor 452 for the crosssslide pump .454. is similar. to theservo motor 451 and includes a polarized solenoid plunger 475, a valveplunger 476, a servovalve 477, a follow up sleeve 478, a power cylinder479, a piston 480 working in the cylinder and operating a piston rod 481connected to the yoke 482 of the variable, displacement pump 454 for thecross-slide, a link 483; connected to an arm 484 fulcrumed at 485and,con-' nected to the piston rod 481 by headed stud 486. Pres:

sure fluid is supplied to the center port of the valve 477 throughpressure line 471 and the end ports of the valvev are connected to thedrain line 81 of the system. The

motor ports of the valve are connected by lines 487 and.

488 to the upper and lower ends,.respectively, of the cylinder 479. IThe servo mechanism for the cross-slide operates in the same manner asthat for the table to adjust the yoke 482 for the cross-slide pump 454inack cordance with the amount of current flowing through the solenoid446 and in a direction corresponding to the;

direction of how of current through the coil.

The variable displacement pump 453 for operating the table 21 of themachine tool operates as a closed system with the hydraulic cylinder 55(FIG. 2.) which, as heretofore explained, actuates the table 21. Thefluid delivery. lines 495 and 496 of the pump are connected to ports:

on selector valve 73 which, when this valve is set for tracer operation,are connected to motor lines 77 and 79 while the servovalve lines 78 and80 will be disconnected. from the cylinder so as to render the handservovalve 7G inefiective.

In a similar manner, the variable displacement pump 454 for thecross-slide is connected by delivery lines 497 and 498 with additionalports on the selector valve 73 so as to cause this pump to be connectedto the cylinder: 58 for the cross-slide through lines 82 and 84 when thevalve is set for tracer operation. At the same time, the] lines 83 and85 from the hand servovalve 71 will be disconnected from the cylinder soas to disable the valve and prevent hand operation of the cross-slide.

The system is protected against overloads by a reliefv valve 500 andcheck valves 501, 502, 503 and 504 in the case of the pump 453, and apressure relief valve 505 and,

check valves 506, 507, 508 and 569 in the case of the pump 454. In thearrangement shown, these valves will by-pass fluid from one side of thepump to the other ifthe pressure in the delivery lines exceeds thepressure setting of the relief valve.

Provision is made for replenishing any fluid loss from.

each of the, pump and cylinder systems due to leakage so that positiveactuation of the table and cross-slide. will be, assured. For thispurpose, the pressure supply line 471 is connected through opposed check.valves5 12 and-513 with the delivery lines 495 and'496, respective.-'ly, and by similarly arranged check valves 514 and 515. with thedelivery lines 497 and 498. Hence, make-up oil will be delivered fromthe pressure line 471 to the low pressure side of the pump in whateverquantity is needed to maintain the system filled with fluid. At the sametime, the check valvm will operate to prevent fluid from the highpressure side of the pump from entering the" pressure line 471.

The pumps 453 and 454 are arranged to be driven at:

varying speeds by power supplied by an electric motor 520 (FIG. 15)which drives the input shaft 521 of a variable speed drive 522 which maybe adjusted by handwheel 519. This drive may be of any desired typewhich will provide a suitable range of speed variation between the inputshaft 521 and an output shaft 523 which drives:

shafts 524 and 525 of the pumps 453 and 454,-respectively, through gears526 and 527 mounted on the pump.

shafts and meshing with a gear 528 secured to the outputshaft 523. Bythis means the feed rate of the cutter rela-; tive to theworkpiece andof the tracing finger relative,

19 to the pattern may be controlled. as desired by adjusting thespeedratio between the input shaft 521 and the output shaft 523 of the drive522 by means of handwheel 519. such as the cam 199 (FIG. of fixeddisplacement so that the sine-cosine voltages produced by thetransformers 195 and 196 are always of the same, magnitude regardlessofthe feed rate employed. This system has a further advantage in thatthe throw of the yokes 463 and 482 (FIG. of the pumps remains the samefor all feed rates thereby eliminating inaccuracies in the operation ofthe tracer control system which would be introduced by attempting tooperate the pumps very close to their positions of zero displacement inorder to obtain. low feed rates.

Throttling control circuit The tracer control mechanism hereinbeforedescribed is provided with means for reducing the feed rate of thecutter relative to the workpiece and of the tracing finger relative tothe pattern when abrupt changes in the pattern outline are sensed by thetracing finger 40 so as to provide time for the tracing finger to rotateand signal a change of direction to the table and cross-slide throughthe sine-cosine transformers. In this way, the feed rate of the machinetool will automatically be adjusted in the manner necessary to permitaccurate reproduction of abrupt corners occurring in the pattern ormaster being traced.

Referring to FIG. 10 of the drawings, the tube 311 which amplifies theerror signal produced by the transformer 174 in response to deviationsof the tracing finger from its position of normal displacement, hasconnectedto its plate one end of a potentiometer winding 535 the otherend of which is connected to ground. The slider of this potentiometer isconnected to the grid of a phase inverter tube 536 the plate and cathodeof which are suitably coupled to the grids of a push-pull amplifier tube537. The plates of this tube are fed from the supply terminal 255through the center tap of the primary winding of a transformer 538. Thecenter tap of the secondary winding of the transformer 538 is maintainedat a predetermined potential with respect to ground by a voltage dividerincluding resistors 539 and 540. The plates of a full-wave rectifiertube 541 are connected to the end terminals of the secondary winding oftransformer 538 while the cathodes of the tube 541 are tied together andconnected to the center tap of the secondary winding through aresistance-capacitance filter network and a load resistor 542 connectedto a line 543 which is joinedto the center tap.

When the machine tool is set for hand servo operation,

the line 543 is connected with thegrid of a bias tube-544 through a pairof normally closed relay contacts 341-1 which are associated with arelay 341 (FIG. 10). This relay also controls a pair of normally opencontacts 341-2 which are connected across the load resistor 542. Whenthe relay 341 is energized, the contacts 341-1 will open and thecontacts 341--2 will close thereby connecting the grid of bias tube 544to the upper end of load resistor 542 in place of to the line 453.

The cathode of tube 544 is connected through a biasing resistor 547 toground and through a line 548 to the cathode of throttle tube 377, thegrid of which is maintained at predetermined potential by a voltagedivider comprised of resistors 549 and 550 connected between the supplyterminal 255 and ground. The screen grid of the throttle tube is held ata constant potential by means of a voltage regulator tube 551' which isenergized from tshge supply terminal through a voltage dropping resistorWhen the machine tool is set for automatic tracer control, the contacts341-1 will be open and the contacts- 3412 will be closed therebyconnecting the grid of bias tube 544 to the output of rectifier tube541. Under these conditions, when the tracing finger 40 is deflecteddue-t0 It is thereby possible to utilize a sine-cosine cam a change indirection. in the pattern outline, the error signal produced by thetransformer 174 and amplified uppcrend of the. resistor positive withrespect to the lead 543. The size of this. voltage drop will beproportional to the magnitude of the error signal. This will cause anincrease in current flow through the bias tube 544 and cause the cathodeof this tube and also the cathode of throttle tube. 377 to'become morepositive. This increases the negative bias on throttle tube 377 therebyreducing the amplitude of the 10,000 cycle energizing voltage deliveredto the primary windings of the sine-cosine differential transformers 195and 196 in proportion to the magnitude of the error signal. Hence, theoutput voltages of the transformers will be correspondingly reducedthereby reducing the displacement of the pumps 453 and 454 which operatethe table and cross-slide of the machine.

M achihe controls Referring to. FIG. 9, it will be seen that power ispro vided for the control circuit of the tracing apparatus by thesecondary winding of a power transformer 562, the primary winding ofwhich is adapted to be, energized from the power line. The lines 565 and566 which are connected to the secondary winding will thereby beenergized and cause. the solenoid 567 of valve 107 (FIG. 2) to beenergizedthrough a normally open limit switch 568, mounted in the.tracing head, which is normally held closed by an adjusting screw 569(FIG. 3) mounted in the right-handend of the lever 168. As previouslyexplained, whenthe solenoid valve 107 is encrgized, the line 106 (FIG.2) is connected to drain thereby permitting the half nut 101 to engagethe feed screw so as to place. the tool head under hand servo control.However, in the event of overdeflection of the tracing finger 40 to apoint where damage to the machine might occur, the adjustment screw 569will permit the contacts of switch 568 to open thereby de-energizingsolenoid valve 107 and connecting line 106 to the high-pressure supplyline 67 of the hydraulic system. This will remove the half nut 101 fromthe feed screw and allow spring 103 (FIG. 2) to move the plunger ofvalve 72 upwardly thereby supplying fluid under pressure through line 86to the upper end of cylinder 61 so as to elevate the tool head and liftthe cutter and tracing finger away from the workpiece and pattern. Afterthe overdeflected condition of, the tracing finger has been eliminated,the switch 568 will again be closed to energize solenoid valve 107 andre-engage the half nut 101 thereby enabling the head to be moved downunder hand servo control.

Referring to FIG. 10 it will be seen that the coil of relay 341 isconnected in the plate circuit of a triode vacuum tube 571 whichcontrols the energization of relay 341. The grid of tube 571 isconnected by a resistor 572 to they plates of a full-wave rectifier tube573 and by a second resistor 574 to ground. The resistors 572 and 574form a load circuit for the tube 573, the cathodes of which areconnected to the end terminals of the. secondary winding of transformer538.

When the tracing finger is. hanging free, a high level error signal isproduced by the difierential transformer 174' which is amplified by thetube 537 andrectified by the tube 573. whose cathodes are connected toground through resistors 575' and,.576. A. negative voltage will therebybe developed across the resistor 574 which will apply a negative bias tothe grid of tube 571 and prevent energization of the coil. of relay 341.However, as soon as the tracing finger is deflected toward its nullposition, the error signal will be diminished thereby reducing thenegative bias on the grid of tube 571 to a point where. sufficientcurrent will be conducted by the tube to energize relay 341. This willcause contacts 341-3 of the relay to close thereby locking the relaythrough a normallyclosed push button switch 50, mounted on the tracinghead 39"(FIG. l),' an1d the voltage dropping resistor 577. 'It will benoted that one of these contacts is connected to ground while the otheris connected to a junction 560 which in turn is connected to oneterminal of switch 50. The junction 560 is also connected to one end ofthe winding of relay 358 (FIG. 9). Hence, the contacts 341-3 will closea circuit through the coil of relay 358 (FIG. 9) to ground and energizethis relay. This will cause the previously mentioned contacts 358'- 2and 358-3 (FIG. 11) of this relay to open and the contacts 358-1 thereofto close. At the same time, a further set of contacts 358-4 controlledby this relay will be closed thereby energizing the solenoid 579 of asolenoid valve 580 (see also FIG. 2). When the valve 580 is energized,fluid will be delivered under pressure through line 581 behind theplunger 74 of the selector valve 73 so as to shift the valve from handservo control position to tracer control position, the chamber at theend of plunger 75 being connected to drain through a line 582. connectedto a port on a hydraulic push button valve 583 having an operatingbutton 584 (see also FIG. 1). The table and cross-slide will now beplaced under the control of the variable displacement pumps of thetracer control system and control of these elements by the hand servovalves 70 and 71 will be disabled. The machine will continue to operateunder -.tracer control until switch 50 is held depressed while thetracing finger is manually steered away from the pattern by grasping theknurled ring 131 (FIG. 3) and turning it forcibly away from the pattern.The finger will now hang free and cause a larger error'signal to beproduced which will bias the grid of tube571, negative and tie-energizerelay 341. This will cause contacts 341-3 (FIG. 9) to open therebydropping out relay 358'. Contacts 358-4 will thus be opened tode-energize solenoid valve 580 and connect line 581 to drain. Contacts358-1 (FIG. 11) will be opened and the machine may now be steered bysimply turning the knurled ring 131 in the direction desired.

If the operator wishes to restore the machine to hand servo control, thehydraulic push button 584 is depressed so as to connect the line 582 tothe pressure line 67 and shift the selector valve 73 to the Handposition. It \m'll be noted that whatever the condition of the machine,when the tracing finger is deflected toward its null position with theswitch 50 in its undepressed position, the relay 341 will pull in andcause the machine to be set for full automatic tracing.

To facilitate setting up the machine for tracer operation, it isdesirable to lock the tracing finger 40 in its vertical position asshown in FIG. 3 and for this purpose a knurled head 586 is provided onthe upper end of the threaded sleeve 186 to permit the sleeve to beturned downwardly until its lower end abuts against the upper edge oflever 168 and locks it against upward movement. This will hold thefinger against displacement until the sleeve is backed off by reverserotation thereof by the operator of the machine. against damage shouldthe operator forget to return the sleeve 186 to the position shown inFIG. 3 where the lever 168 is free to move upwardly under the control ofthe finger to control operation of the machine in theintended manner, alimit switch 564 is placed in the tracing head so that the normallyclosed contacts of the switch will be opened when the sleeve 186 isturned down to lock the finger. As shown in FIG. 5, the switch 564 ismounted on the body 171 immediately beneath a flange 587 formed on theupper end of sleeve 186. The operating button of the switch lies incontact with the bottom surface of the flange and will be depressedthereby when the sleeve is screwed down into the block so as to open thecontacts of the switch. The switch 564 is preferably located in thecontrol circuit of the pump driving motors 64 (FIG. 2) and 520 (FIG. 15)so as to disable the motors To safeguard the mechanism 22 while theswitch is open and thereby prevent opeiation of the machine while thetracing finger is locked.

Operation The tracer controlled machine tool heretofore described lationof hand wheels 45 and 46 thereby causing the dif-.

ferential transformer 174 (FIG. 3) to approach its null position. Thiswill decrease the bias on relay tube 571 (FIG. 10) and causerelay 341 topull in and close con- I tacts 341-3 (see also FIG. 9) so as to lockinthe relay and energize relay 358. The latter relay, when energized,closes contacts 358-4 and energizes solenoid valve 580 (FIG. 2) so as toshift selector valve 73 from Hand position to Tracer position Asheretofore explained this will cause the table and cross-slide cylinders55 and 58, respectively, to be connected in a closed system with thevariable displacement pumps 453 and 454 and render inelfective thecontrol of the cylinders by hand servo-,

valves 70 and 71. Energization of the relay 358 also causes contacts358-2 and 358-3 (FIG. 11) to open, and contacts 358-1 in the platecircuit of power ampli fier tubes 351 and 352 to close, therebyconditioning the rotation control circuits for operation.

An alternative method of engaging the finger with the pattern is tomanually deflect the tracing finger so as to condition the machine forfull automatic tracing, and then release the finger with the switch 50depressed. This will cause the relays 341 and 358 to drop out, aspreviously explained, but will allow the selector valve 73 to remain inTracer position. The finger may now be steered into contact with theedge of the pattern by suitable manipulation of knurled ring 131. Assoon as the finger is deflected by the pattern, it will cause the relaysto pull in and thereby condition the machine for full automatic tracing.

Referring to the block diagram of the tracer control system shown inFIG. 14, as herein indicatedthe templet 41 acts on the tracer finger 40to deflect it from its vertical or free position as shown in FIG. 3. Thetracing finger controls the rotation transformer or pickup 174 to whichis fed an energizing voltage produced by the oscillator and filter 284.As heretofore explained, this voltage is applied to the primary windingof the transformer and an error signal is produced on the outputterminal of the secondarywindings whenever the tracing finger isoverdeflected or underdeflected from its normal or null position. Theerror signal is amplified by tube 311 (FIG. 10). and push-pull amplifiertube 320 (FIG. 11) after which it is passed to the discriminatingcircuit including tube 330 for the purpose of ascertaining the phase ofthe error signal. The discriminated signal is then rectified by tube 333and amplified by DC. amplifier 334 to provide a DC signal the sign ofwhich corresponds to the phase of the error signal. This signal isapplied to the grids of a push-pull DC. power amplifier comprised oftubes'351 and 352 (see also FIG. 14) which controls the energiza-lmanner as to change the directional heading of the cutter

